Electronic mice are well known for their advantages as pointing devices. Basically, an electronic mouse converts the linear movement of the mouse over a surface into digital signals to control the cursor of the computer. One common type of electronic mouse uses an optomechanical interface, whereby the movement of a ball drives at least two shaft encoders. The shaft encoders in turn drive an encoding wheel located between a photosource and a photodetector. The movement of the encoding wheel causes pulses of light to reach the photodetector, which creates a pulse train indicative of movement of the mouse.
To provide accurate correlation between the movement of the mouse and movement of the cursor, the ball in an optomechanical mouse must be supported within fairly close tolerances. In substantial part, these close tolerances are necessary to maintain the ball in constant contact with the shaft encoders. In most such mice, a ball cage is provided to maintain the ball in proper position, and the shaft encoders are integrated into the ball cage. In the past, the ball cage has been a complicated assembly comprising in excess of twenty parts, including multiple parts for the shaft encoders and related mechanical elements, a pressure roller to maintain the ball in contact with the shaft encoders, and the ball cage itself. Also, a traction spring with hooks, which is comparatively difficult to assemble, has been required by many prior designs.
Such complicated assemblies increase manufacturing costs and reduce reliability. In addition, prior art designs typically do not lend themselves to use in automatic assembly. There has therefore been a need for a simple ball cage configuration which provides at least equal accuracy while reducing complexity and part count and permitting automatic assembly.